Identifications of program types are provided in the radio data system, defined in the beginning of 1984 and in the meantime established between radio stations and appropriately equipped radio receivers. RDS data transmission include 104 bit long "groups" of 26-bit "blocks", which reserve several bits in block 2 for a Program TYpe or PTY code. Item 4.3 of the system definition states that the identification makes it possible to program receivers in such a way that they only react to those programs which correspond to the desired type, i.e. reproduce only these via the loudspeaker. See page 30.
As a rule, there is only limited space with a narrow access surface available for installing car radios in motor vehicles. Following installation of the car radio, this access surface is covered by the instrument cover. However, the surface of this instrument cover has only sufficient space for a small number of operating elements. For this reason it is known to assign to either individual or all operating elements different switching functions regarding the various modes, in the form of a so-called mode switch, and to indicate the respectively switched-on mode on the display of the car radio.
The actuation of one of the operating elements during the active state in a certain mode is stored in the memories associated with the modes. Subsequently another mode can be selected by means of the mode switch without the previously set selection of the operating element being lost. To change the operation in the mode which was first selected, it is necessary to recall this first-selected mode by means of the mode switch.